sclass WithReasoning<A> extends Var<A> {
  S reasoning;
  
  *() {}
  *(A value) { super(value); }
  *(A value, S *reasoning) { super(value); }
  
  toString {
    if (empty(reasoning)) ret super.toString();
    ret super.toString() + "\n" +
      indentx("[Reasoning: " + reasoning + "]");
  }
}